Methods and devices of the general type under consideration are used in commercial vehicles for spacing-control systems and speed-control systems that set a speed value or acceleration value as a function of the vehicle traveling ahead. These feedback control systems are also designated as spacing/speed controllers or automatic distance regulators (ADR), in which connection the expression “adaptive cruise control” (ACC) has also gained acceptance for such feedback control.
Adaptive spacing-control and speed-control systems are capable of accessing the braking system and/or the engine management system, so that by accelerating and/or decelerating the vehicle a desired target spacing from the vehicle traveling ahead can be adjusted automatically. Consequently, the general driving safety is enhanced by maintaining a sufficient distance from the vehicle traveling ahead, and the brake wear and hence also the vehicle breakdown-times are reduced.
Such feedback control systems are advantageous when monotonous driving maneuvers, which can lead to fatigue and consequently to a reduced ability of the vehicle driver to react, have to be performed over and beyond a relatively long period. Monotonous and tiring driving maneuvers frequently have to be performed in the course of transportation journeys involving commercial vehicles, or in the course of driving urban buses or tour coaches.
DE 10 2010 055 373 A1 describes a method for controlling longitudinal dynamics of a motor vehicle in accordance with an adaptive spacing-control or speed-control system.
Longitudinal-dynamics behavior of a motor vehicle regulated by ACC is greatly dependent on environmental influences such as the inclination of the road or the wind conditions, for example. Accordingly, in the case of conventional feedback control systems, it can be observed that during level travel in succession a high degree of ride comfort can be guaranteed, and the desired headway from the vehicle traveling ahead can be maintained satisfactorily. However, if, as a consequence of inclination of the road during travel downhill, the vehicle undergoes an additional acceleration that is not dependent on the drive torque of the engine, the feedback control system can no longer maintain the high degree of ride comfort, and/or the set or desired spacing from the vehicle traveling ahead can no longer be maintained. Undershooting the desired headway can result in a sudden and strong braking intervention of the feedback control system, or the driver may feel compelled by subjective sensation to intervene by braking, resulting in further discomfort. Consequently, known systems can also be set such that a high degree of ride comfort is guaranteed during travel on an incline; however, this is at the expense of maintaining comfort during level travel.
There is therefore a need for an adaptive spacing-control or speed-control system that can be put into effect economically and that guarantees a high level of comfort and sufficient headways both in the course of level travel and during travel downhill.